i) Field of the Invention
The present invention relates to a phase shit mask which can enhance a resolution of a transfer pattern by utilizing an interference action caused to occur among light waves in a phase shifter. In particular, the present invention relates to a material of the phase shift mask, and a method of manufacturing the phase shift blank and mask, and more particularly to a halftone phase shift mask, blank, and a method of manufacturing the halftone phase shift mask and blank.
ii) Description of Related Art
For DRAM, a mass production system of 256 Mbits has been established at present, and a higher integration to a gigabit grade from a megabit grade is going to be attempted nowadays. Accordingly, a design rule of an integrated circuit has increasingly been minute. It is a matter of time that a fine pattern with a line width (half pitch) of 0.10 xcexcm or less is demanded.
As one means for handling such a fine pattern, a resolution of the pattern has been improved by shortening a wavelength of an exposure light source. As a result, a KrF excimer laser (248 nm) or an ArF excimer laser (193 nm) is mainly used in the exposure light source in an existing photolithography method.
Although the shortened exposure wavelength improves the resolution, a depth of focus becomes shallow. Therefore, a heavy burden tends to be imposed onto a design of an optical system including a lens, or adverse influences such as deterioration of stability of a process takes place in such a design.
To solve the problems, a phase shift method has been used, in the phase shift method, a phase shift mask is used as a mask for transferring the fine pattern.
The phase shift mask is constituted, for example, of a phase shifter portion that serves as a pattern portion on the mask, and a non-pattern portion in which the phase shifter portion does not exist. A phase of light transmitted through both the portions is shifted by 180xc2x0 relative to each other, then mutual interference of light, namely, light waves is caused to occur at pattern boundary portions. This is effective to enhance contrast of a transferred image. It is known that a phase shift amount xcfx86 (rad) of a light wave passed through the phase shifter portion depends on a real part n of a complex refractive index and a film thickness d of the phase shifter portion and that a relationship of the following equation (1) is established.
xcfx86=2xcfx80d(nxe2x88x921)/xcexxe2x80x83xe2x80x83(1)
Here, xcex denotes a wavelength of an exposure light. Therefore, to shift the phase by 180xc2x0, the film thickness d may be set as follows.
d=xcex/{2(nxe2x88x921)}xe2x80x83xe2x80x83(2)
The phase shift mask achieves an increase of the depth of focus for obtaining a necessary resolution, and it is possible to establish both improvement of the resolution and enhancement of applicability of the process without changing the exposure wavelength.
The phase shift mask is practically roughly classified into a perfect transmission (Levenson type) phase shift mask and a halftone phase shift mask in accordance with a light transmission property of the phase shifter portion forming a mask pattern. The former has a transmittance of the phase shifter portion which is equal to that of the non-pattern portion (light transmission portion), and is a mask substantially transparent to the exposure wavelength. It is generally said that the mask is effective for transferring a line and space. On the other hand, in the latter halftone type, the phase shifter portion (light semi-transmission potion or light translucent portion) has a transmittance of about several percentages to several tens of percentages, as compared with the transmittance of the non-pattern portion (light transmission portion). It is said that the halftone type is effective for preparing a contact hole or an isolated pattern.
An example of the halftone phase shift masks includes a single-layer type halftone phase shift mask which is simple in structure and which is easy to manufacture. Such single-layer halftone phase shift masks can be exemplified by SiOx-based and SiOxNy-based masks described in Japanese Patent Application Laid-Open No. 199447/1995, SiNx-based mask described in U.S. Pat. No. 5,477,058, and the like.
In order to achieve higher integration by the photolithography method in future, even by using the phase shift method, It is still necessary to further shorten the exposure wavelength. As a next-generation exposure light source following the KrF excimer laser and ArF excimer laser, F2 excimer laser (157 nm) has already been tried and investigated. However, shortening the wavelength of the exposure light source imposes the burden onto the optical system as described above, and also brings about difficulty in development/preparation of a photo mask. As a result, development of the halftone phase shift mask for the F2 excimer laser has hardly been started in the present situation. The following will be made about causes of the problems hereinafter.
First in many solid materials, a degree of light absorption increases as the wavelength becomes short. Taking this into account, it is assumed that a transmission film material and a translucent film material which are used in the KrF excimer laser and ArF excimer laser may be applied to the halftone phase shift mask for the F2 excimer laser. In this event, a film should be thick in order to obtain a predetermined phase angle. As a result the transmittance substantially indicates a value close to zero. Moreover, when the degree of absorption of the exposure light is high, the film forming the phase shifter portion is liable to suffer from damages by the exposure light. The damages herein mean changes of optical properties (transmittance, refractive index, and the like) of the film, film thickness change, film properties deterioration, and the like because of a defect generated in the film forming the phase shifter portion by absorption of the exposure light, and a cleavage in a bond.
Additionally, consideration should also be made as a film material of the phase shifter portion about problems, such as etching selectivity of the phase shifter film influencing a processing precision, a chemical durability to acid or alkali used in a cleaning step of a manufacturing process, and the like.
The present invention has been developed under the aforementioned background, and an object thereof is to provide a halftone phase shift mask which can be used in an exposure wavelength range of 140 nm to 200 nm including a wavelength of an F2 excimer laser of 157 nm, and a halftone phase shift mask blank for forming the halftone phase shift mask.
To achieve the aforementioned object, the present inventor et al have performed an intensive research/development. As a result, it has been found out that SiNx makes a matrix of a film dense by the virtue of an Sixe2x80x94N bond. This brings about the facts that SiNx has a high irradiation durability against an exposure light and a high chemical durability against detergent or the like. On the other hand, SiOx has a relatively high transmittance even on a short wavelength side. Under the circumstances, attention has been directed to SiOxNy that has advantages of both materials mentioned above. Furthermore, it has been found that using SiOxNy makes it possible to obtain a phase shifter film suitable for use in an exposure light having a short wavelength by controlling a composition of SiOxNy. The present invention has been made in consideration of the above-mentioned facts.
Now, the phase shifter film is basically different in a composition range from a conventional SiOxNy-based film, and is further different in film properties (e.g., physical properties such as k) from the conventional SiOxNy-based film. A combination of the composition range and film properties can realize a phase shifter film which has a transmittance of 3 to 40% and a refractive index (related to a film thickness for shifting the phase by a predetermined angle) of 1.7 or more in the vicinity of the wavelength of the F2 excimer laser of 157 nm. Moreover, the phase shifter film is satisfactory in irradiation durability to exposure light and chemical durability.
Furthermore, when the phase shifter film is constituted in the form of a double-layer structure of an SiOxNy film and an etching stopper film, a phase shifter film is satisfactory not only in the irradiation durability to exposure light and chemical durability but also in workability of a pattern.
The present invention has the following constitutions.
(Constitution 1) A halftone phase shift mask blank is for use in manufacturing a halftone phase shift mask which has a transmission portion for transmitting an exposure light, and a phase shifter portion for transmitting a part of the exposure light and for shifting a phase of the transmitted light by a predetermined amount on a transparent substrate and in which an optical property is designed so as to mutually cancel out the respective transmitted lights in the vicinity of a boundary portion of the transmission portion and the phase shifter portion and thereby a contrast of a boundary portion of an exposure pattern transferred onto the surface of a material to be exposed can satisfactorily be held and improved, and having a phase shifter film for forming the phase shifter portion on the transparent substrate,
wherein the phase shift mask is used in an exposure light wavelength range of 140 nm to 200 nm,
the phase shifter film is constituted of a film containing main constituting elements of silicon, oxygen, and nitrogen, and contains 35 to 45% of silicon, 1 to 60% of oxygen, and 5 to 60% of nitrogen in atomic percentage, and a total amount of these elements occupies at least 90% or more of a whole composition constituting the phase shifter film.
(Constitution 2) A halftone phase shift mask blank for use in manufacturing a halftone phase shift mask which has a transmission portion for transmitting an exposure light, and a phase shifter portion for transmitting a part of the exposure light and for shifting a phase of the transmitted light by a predetermined amount on a transparent substrate and in which an optical property is designed so as to mutually cancel out the respective transmitted lights in the vicinity of a boundary portion of the transmission portion and the phase shifter portion and thereby a contrast of a boundary portion of an exposure pattern transferred onto the surface of a material to be exposed can satisfactorily be held and improved, and having a phase shifter film for forming the phase shifter portion on the transparent substrate,
wherein the phase shift mask is used in an exposure light wavelength range in the vicinity of 157 nm as a wavelength of an F2 excimer laser,
the phase shifter film is constituted of a film containing main constituting elements of silicon, oxygen, and nitrogen, and contains 35 to 40% of silicon, 25 to 60% of oxygen, and 5 to 35% of nitrogen in atomic percentage, and a total amount of these elements occupies at least 90% or more of a whole composition constituting the phase shifter film.
(Constitution 3) A halftone phase shift mask blank for use in manufacturing a halftone phase shift mask which has a transmission portion for transmitting an exposure light, and a phase shifter portion for transmitting a part of the exposure light and for shifting a phase of the transmitted light by a predetermined amount on a transparent substrate and in which an optical property is designed so as to mutually cancel out the respective transmitted lights in the vicinity of a boundary portion of the transmission portion and the phase shifter portion and thereby a contrast of a boundary portion of an exposure pattern transferred onto the surface of a material to be exposed can satisfactorily be held and improved, and having a phase shifter film for forming the phase shifter portion on the transparent substrate,
wherein the phase shift mask is used in an exposure light wavelength range in the vicinity of 193 nm as a wavelength of an ArF excimer laser,
the phase shifter film is constituted of a film containing main constituting elements of silicon, oxygen, and nitrogen, and contains 38 to 45% of silicon, 1 to 40% of oxygen, and 30 to 60% of nitrogen in atomic percentage, and a total amount of these elements occupies at least 90% or more of a whole composition constituting the phase shifter film.
(Constitution 4) A halftone phase shift mask blank for use in manufacturing a halftone phase shift mask which has a transmission portion for transmitting an exposure light, and a phase shifter portion for transmitting a part of the exposure light and for shifting a phase of the transmitted light by a predetermined amount on a transparent substrate and in which an optical property is designed so as to mutually cancel out the respective transmitted lights in the vicinity of a boundary portion of the transmission portion and the phase shifter portion and thereby a contrast of a boundary portion of an exposure pattern transferred onto the surface of a material to be exposed can satisfactorily be held and improved, and having a phase shifter film for forming the phase shifter portion on the transparent substrate,
wherein the phase shift mask is used in an exposure light wavelength range of 140 nm to 200 nm,
the phase shifter film is constituted of a film containing main constituting elements of silicon, oxygen, and nitrogen, a complex refractive index real part n of the phase shifter film with respect to the exposure light is 1.7 or more, and a complex reflective index imaginary part k is 0.450 or less.
Here, the aforementioned n, k have the following relation with an energy transmittance T of the mask, an energy reflectance R, a film thickness d of the phase shifter portion of the mask, and a refractive index n0 of the mask substrate.       R    =                  r        ⁢                  xe2x80x83                ⁢                  r          _                ⁢                  xe2x80x83                ⁢        r            =                                                                  ρ                1                            +                                                ρ                  2                                ⁢                                  ⅇ                                                            -                      2                                        ⁢                                          xe2x80x83                                        ⁢                    δ                                                                                      1              +                                                ρ                  1                                ⁢                                  ρ                  2                                ⁢                                  e                                                            -                      2                                        ⁢                    δ                                                                                ⁢                      xe2x80x83                    ⁢                      ρ            1                          =                                                                              (                                      n                    -                    ik                                    )                                -                1                                                              (                                      n                    -                    ik                                    )                                +                1                                      ⁢                          xe2x80x83                        ⁢                          ρ              2                                =                                                    (                                  n                  -                  ik                                )                            -                              n                0                                                                    (                                  n                  -                  ik                                )                            +                              n                0                                                              δ    =                                                      2              ⁢                              xe2x80x83                            ⁢              π              ⁢                              xe2x80x83                            ⁢              nd                        λ                    ⁢                      xe2x80x83                    ⁢          T                ≃                  t          ⁢                      xe2x80x83                    ⁢                      t            _                    *                      1                          n              0                                ⁢                      xe2x80x83                    ⁢          t                    =                                    τ            1                    ⁢                      τ            2                    ⁢                      ⅇ                                          -                                  xe2x80x83                                ⁢                1                            ⁢              δ                                                1          +                                    ρ              1                        ⁢                          ρ              2                        ⁢                          ⅇ                                                -                  2                                ⁢                                  xe2x80x83                                ⁢                i                ⁢                                  xe2x80x83                                ⁢                δ                                                                    τ      1        =                            2                      1            +                          (                              n                -                ik                            )                                      ⁢                  xe2x80x83                ⁢                  τ          2                    =                        2          ⁢                      xe2x80x83                    ⁢                      n            0                                                n            0                    +                      (                          n              -              ik                        )                              
Herein, {overscore (r)}, {overscore (t)} denote conjugated complex numbers of r, t, respectively.
(Constitution 5) A halftone phase shift mask blank for use in manufacturing a halftone phase shift mask which has a transmission portion for transmitting an exposure light, and a phase shifter portion for transmitting a part of the exposure light and for shifting a phase of the transmitted light by a predetermined amount on a transparent substrate and in which an optical property is designed so as to mutually cancel out the respective transmitted lights in the vicinity of a boundary portion of the transmission portion and the phase shifter portion and thereby a contrast of a boundary portion of an exposure pattern transferred onto the surface of a material to be exposed can satisfactorily be held and improved, and having a phase shifter film for forming the phase shifter portion on the transparent substrate,
wherein the phase shifter film is constituted of a film containing main constituting elements of silicon, oxygen, and nitrogen, and an etching stopper film formed between the film and the transparent substrate.
(Constitution 6) The halftone phase shift mask blank according to Constitution 5 wherein the etching stopper film has a function for adjusting a transmittance.
(Constitution 7) The halftone phase shift mask blank according to Constitution 5 or 6 wherein the etching stopper film is a material which can be etched with an etching medium different from an etching medium of the film containing main constituting elements of silicon, oxygen, and nitrogen.
(Constitution 8) The halftone phase shift mask blank according to Constitution 5 or 6 wherein the etching stopper film is a material which can be etched with the same etching medium as an etching medium of the film containing the main constituting elements of silicon, oxygen, and nitrogen.
(Constitution 9) The halftone phase shift mask blank according to any one of Constitutions 5 to 8 wherein the phase shift mask is used in an exposure light wavelength range of 140 nm to 200 nm.
(Constitution 10) The halftone phase shift mask blank according to any one of Constitutions 5 to 9 wherein the film containing the main constituting elements of silicon, oxygen, and nitrogen contains 30 to 45% of silicon, 1 to 60% of oxygen, and 5 to 60% of nitrogen in the atomic percentage, and the total amount of these elements occupies at least 90% or more of the whole composition constituting the film.
(Constitution 11) A method in which the halftone phase shift mask blank according to any one of Constitutions 1 to 10 is manufactured,
said method comprising steps of: using sputtering gases such as an inactive gas, an oxygen gas, and a nitrogen gas to sputter the film containing the main constituting elements of silicon, oxygen, and nitrogen in a reactive sputtering process; and setting a ratio of oxygen in said sputtering gas to a range of 0.2 to 30%.
(Constitution 12) A halftone phase shift mask which has a mask pattern constituted of a light transmission portion and a phase shifter portion and obtained by subjecting the phase shifter film in the halftone phase shift mask blank according to any one of Constitutions 1 to 11 to a patterning treatment to selectively remove the phase shifter film and obtain a predetermined pattern.
(Constitution 13) A pattern transfer method in which the halftone phase shift mask according to Constitution 12 is used to transfer the pattern.